The present invention relates to a spindle nut for a ball screw and also to a ball screw with a spindle nut arranged on a threaded spindle, and also to an electromechanical brake booster provided with a ball screw for the operating brake of a motor vehicle. A ball screw has a threaded spindle and a spindle nut arranged on the threaded spindle, wherein balls are arranged between the threaded spindle and the spindle nut. A relative rotational movement between the spindle nut and the threaded spindle is converted into a translational movement between the spindle nut and the threaded spindle.
From EP1134455A1, for example, a ball screw was known, whose spindle nut has a nut part on whose inner periphery a spiral ball groove wound about a spindle axis is formed for the rolling of the balls. This spindle nut is provided with deflection elements for deflecting the balls, wherein the nut part has two recesses that are arranged spaced axially apart from each other and in each of which there is one of the deflection elements. The nut part is provided with a straight return channel formed as a return bore for the balls, wherein the straight return channel connects the two recesses to each other and wherein the straight return channel is arranged within the wall thickness of the spindle nut. The balls roll along a ball track that is formed by the return channel and the deflection elements. The straight return channel is arranged axis-parallel to the spindle axis. Due to the geometric position of the straight return channel and the curved deflection channel, the balls are subject to considerable acceleration when they enter into the curved deflection channel, wherein this acceleration can cause undesired friction losses in the contact of the balls with each other, which can result in the balls stalling in the ball channel and thus a fluctuation in the efficiency.
The recesses in the nut part each comprise two surfaces running essentially orthogonal to the longitudinal axis of the threaded spindle and also two concave surfaces essentially parallel to the longitudinal axis of the threaded spindle. These orthogonal surfaces reach up to the inner periphery of the nut part. The bearing capacity of the ball groove formed on the inner periphery of the nut part is lessened in the area of the return channel in any case in an edge area between the inner peripheral surface of the nut part and the orthogonal surface of the recess.